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Nonlinear Structural Materials Module

New App: Stress Analysis of a Pressure Vessel

A pressure vessel is designed to hold liquids or gases at substantially higher or lower pressures than the ambient pressure. A high pressure difference requires a correct design in order to avoid catastrophic failures.

The Stress Analysis of a Pressure Vessel app is an example of how you can design a tool for checking a family of components with a parameterizable geometry. The purpose of the app is to determine if the vessel will be able to sustain the applied internal pressure without exceeding a specified limit on the volume fraction of the material, which has exceeded the yield limit. The app solves for orthotropic plasticity using the Hill Orthotropic Criterion.

You can adjust the geometric parameters of the vessel, internal pressure, material properties, and the volume fraction of the vessel that is allowed to exceed the yield limit. Results from the app include the pressure at which initial yield occurs, the yielded volume fraction below the allowed limit, and the pressure at which the yielded volume fraction reaches the specified limit.

The user interface of the Stress Analysis of a Pressure Vessel app, showing the stress results.

The user interface of the Stress Analysis of a Pressure Vessel app, showing the stress results.

Improved Formulation for Small Strain Plasticity with Geometric Nonlinearity

You can now use a small plastic strain formulation for significantly larger strains without significant loss of accuracy. When you select Small plastic strains as the plasticity model in the Plasticity node, and the study incorporates geometric nonlinearity, the Cauchy stress tensor is used to evaluate the yield function and plastic potential. In earlier versions of the software, the second Piola-Kirchhoff stress tensor was used instead, which limited the useful strain range to a few percent. The Large plastic strains option, available since an earlier release of COMSOL Multiphysics, is more accurate but computationally more expensive. With the new formulation for small plastic strains, the limit for when the full large strain formulation is needed increases from a strain of a few percent to 20% or more, depending on the required accuracy.

Stresses during elastoplastic compression of a pipe, with both a small (left) and large (right) plastic strain assumption.

Stresses during elastoplastic compression of a pipe, with both a small (left) and large (right) plastic strain assumption.